Since the 1800s, pressure gauges have been reliable, accurate, and overall crucial components of most processing systems because they are easy to read to help prevent failure in everyday operations from HVAC, aviation, healthcare, defense, and agriculture. Therefore, how a gauge is constructed and tested is extremely important for reliability, safety, and peace-of-mind. ASME B40.100-2022: Pressure Gauges And Gauge Attachments details the specifications for pressure gauges and gauge attachments.
Importance of Pressure Gauges
A pressure gauge is a method of measuring fluid, gas, water, or steam intensity in a pressure powered machine to ensure there are no leaks or pressure changes that would affect the performance of the system. Any deviation from the acceptable norms in the specific pressure range of the pressure system can seriously impair the workings of that system. Pressures gauges can be used for troubleshooting (i.e., if leaks or block occur in the circuit, the system pressure will reduce) and engineers and technicians can identify the reason for that pressure drop and repair it right away.
Because they are analog, there are no wires and no electricity is needed to operate them. This means if there is a loss of power, the gauge will continue to provide local measurements as it is not susceptible to power outages or voltage fluctuation. Thus, the pressure gauge is essential in analyzing the pressure through the circuit to ensure the system functions properly and safely for its operators.
What Is ASME B40.100-2022?
ASME B40.100-2022 covers analog, dial-type gauges. By using elastic elements, these gauges mechanically sense pressure and indicate it by means of a pointer moving over a graduated scale. The standard defines a pressure gauge as a device that senses and indicates pressure using ambient pressure as datum. ASME B40.100-2022 also includes the following attachments installed between the pressure source and gauge(s):
- Diaphragm seals
- Pressure limiting valves
Devices commonly known as snubbers, pulsation dampeners, pressure equalizers, gauge protectors, or gauge savers, are used to improve the output or readability of the instrument, and to reduce the effect of pressure surges on the instrument. The hazard potential increases at higher operating pressure and the pressure-sensing element in most gauges is subjected to high internal stresses, so these attachments are available for use in these potentially hazardous pressure systems.
Measuring Gauge Pressure
Gauge pressure is the pressure measured in relation to ambient atmospheric pressure. Gauge pressure is positive for pressures above atmospheric pressure; it is negative for pressures below it. The most common pressure reference is a gauge pressure dial, which is signified by a ‘g’ after the pressure unit (e.g., 30 psig). Changes in the atmospheric pressure due to weather conditions or altitude directly influence the output of a gauge pressure sensor. A gauge pressure higher than ambient pressure is referred to as positive pressure.
ASME B40.100-2022 Pressure Gauge Construction
The standard specifies many various specifications and requirements during the construction of pressure gauges, such as:
- Cases may be fabricated from various materials using various manufacturing processes. They may have solid fronts or open fronts and may or may not employ various case pressure relief means.
- Dials shall indicate the units [international system of units (SI); meter, kilogram-force, second, ampere (MKSA); and customary (inch, pound-force, second, ampere)] in which the scale is graduated.
- The recommended graduated Scale Arc is 270 degrees, although special applications and ranges may require scale arcs greater or less than 270 degrees.
- Graduations shall not extend beyond the calibrated portion of the scale.
- The Pointer shall rotate clockwise for increasing positive pressure and counterclockwise for increasing negative pressure
- The tip of the Pointer shall cover 10% to 90% of the minor graduation. The pointer may overlap the graduations.
- Before the installation of a pressure gauge, consideration should be given to environmental conditions such as temperature, humidity, vibration, pulsation, and shock and the possible need for protective attachments, maintenance, and/or special installation requirements.
- Pressure gauges shall be subjected to Salt Spray Tests in accordance with ASTM B117.
ASME B40.100-2022: Pressure Gauges And Gauge Attachments is available on the ANSI Webstore.